const a = ["one", , , "two"];
console.log(a); // [ 'one', <2 empty items>, 'two' ]
console.log(a.pop()); // two
console.log(a); // [ 'one', <2 empty items> ]
console.log(a.pop()); // undefined
console.log(a); // [ 'one', <1 empty item> ]
